1. Field of the Invention
The present invention relates to a protective layer for TiAl materials for affording protection against oxidation and also to a method for producing a corresponding protective layer.
2. Discussion of Background Information
TiAl materials, which are known as metal alloys comprising the main constituents titanium and aluminum, e.g. titanium aluminide alloys, are materials of interest for internal combustion engines or turbomachines, such as stationary gas turbines or aero engines, since they can have high strengths and a good high-temperature stability given a low specific weight. Accordingly, materials of this type are already used in turbomachines. The operating temperature is limited, however, since the TiAl materials usually have inadequate oxidation resistance at relatively high temperatures of above 750° C.
Accordingly, attempts have already been made to develop oxidation-resistant layers for TiAl materials in order to make it possible to increase the corresponding operating temperatures. One example is given in DE 10 2007 060254 A1, the entire disclosure of which is incorporated by reference herein, which describes a platinum-based high-temperature protective layer for aluminum-rich titanium alloys and titanium aluminides.
However, the results which can be achieved with corresponding protective layers particularly at operating temperatures of up to 900° C. and above are still unsatisfactory.
In particular, in the case of known oxidation-resistant layers, various oxidation products may nevertheless form which prevent the formation of a readily adhering and slowly growing oxide layer, which would form protection against further oxidation and a diffusion barrier for oxygen. The diffusion of oxygen can lead to phase transformations in the marginal zone of the component and embrittlement of the base material, and this can impair the mechanical properties of the component. The embrittled marginal zone can continue to grow continuously during use at high temperatures, and therefore the reduction in strength and in particular fatigue strength continues, with the result that the service life of such components is limited.
Moreover, the application of the oxidation-resistant layer may likewise involve damaging oxidation of the TiAl material and diffusion of oxygen or of other constituents of the coating, and this can likewise lead to marginal embrittlement of the TiAl component.
In view of the foregoing, it would be desirable to have available a protective layer for TiAl materials for affording protection against oxidation and oxygen diffusion and also a method for the production thereof, which makes it possible to reliably protect the TiAl material against oxidation and marginal embrittlement at temperatures of above 750° C., in particular up to 900° C. At the same time, it should be possible for the layer to be applied reliably and easily, and the correspondingly coated components should afford long-lasting and reliable protection during operation.